Ion-cement hydrate interactions govern multi-ionic transport model for cementitious materials

Abstract

The main objective of this investigation is to describe the interaction between cement hydrates and electrolyte solution to understand multi-ionic transport in cementitious materials. A surface complexation model in PHREEQC including an electrostatic term is used to simulate the ionic adsorption on the calcium silicate hydrate (C-S-H) surface. The equilibrium constants for the adsorption of ions on C-S-H surfaces are obtained by fitting experimental data to the model. The adsorption of both divalent and mono-valent cations, and also anions significantly changes the surface charges of hydrated paste. Chloride is being held in a chemical binding as Friedel's salt and bound mainly by the adsorptive action of C-S-H. An integrated modelling approach employing a phaseequilibrium model, a surface complexation model, and a multi-component diffusion model has been developed in PHREEQC to simulate the multi-ionic transport through hydrated cement paste. It was found that the physical adsorption of ions on C-S-H, the size of pores, and the surface site density of C-S-H govern the rate of penetration of ionic species. Finally, the proposed model has been validated against chloride profiles measured in this study as well as with data available in the literature for hydrated cement paste.

Development and Verification of an Integrated Physicochemical and Geochemical Modelling Framework for Performance Assessment of Cement-Based Materials

“…On the other hand, PHREEQC can perform geochemical and speciation calculation (Appelo and Postma 2009;Parkhust and Appelo 1999). Furthermore, it can perform the same kind of calculations in cementitious materials as well (Elakneswaran et al 2010;Hosokawa et al 2011;Kari et al 2013). However, PHREEQC cannot predict the hydration or micro-pore structure formation in cementitious materials.…”

“…Reactive transport models are an essential tool to evaluate the performance of cementitious materials because the degradation has to be predicted precisely with time at each point of the materials. In recent years, many reports have been published on multispecies transport and coupling of the transport model with chemical reactions (Elakneswaran et al 2010;Hosokawa et al 2011;Kari et al 2013;Marchand et al 2002). The STADIUM model developed by Marchand et al (2002) coupled the mass and energy transport equations with the chemical equilibrium equation at each step of the calculation.…”

“…Several numerical models have been developed in the past to predict the long-term performance of cementitious materials in aggressive environments (Elakneswaran et al 2010;Hosokawa et al 2011;Ishida et al 2009;Maekawa et al 2009;Marchand et al 2002). These models are improving with understanding the deterioration phenomena through different aspects of the mechanisms and coupling between them.…”

“…Hosokawa et al (2011) proposed a model for multispecies diffusion (Nernst-Planck-Poisson) by considering the chemical reactions between cement hydrates and the pore solution (coupling phase equilibrium model in PHREEQC externally). Multispecies transport can be simulated in PHREEQC only by using the phaseequilibrium and multi-component diffusion modules (Elakneswaran et al 2010;Kari et al 2013). However, in the existing models, different transport parameters and physicochemical properties of the cementitious material such as cement hydrates, porosity, etc.…”

The Impact of Tortuosity on Chloride Ion Diffusion in Slag-Blended Cementitious Materials

“…Furthermore, a relationship between the slag replacement ratio and tortuosity was derived. The determined tortuosity values were incorporated into the reactive transport model developed previously (Elakneswaran et al 2010) to predict chloride transport slag-blended cementitious materials. Thermodynamic equilibrium reactions between hydrates and solution, binding of chloride on hydrates (both C-S-H and monosulfate), and the influence of surface charge on multi-species transport were also considered in the reactive transport model in addition to porosity, pore size and tortuosity effects.…”